Blend the chestnuts and water in a blender until obtaining a soft and smooth cream. Pour into a pot and set aside.
Blend the strawberries until obtaining a purée and pass through a sifter. Add to the chestnut cream.
Incorporate ½ cup of sugar, vanilla extract and agar-agar. Put over medium heat and bring to a boil, whisking constantly.
Remove from the heat and pour into small bowls or glasses. Allow to cool for at least 3 hours.
For the sauce, put the ingredients in a pot and boil for 6 minutes. Remove and strain to remove the fiber.
Serve the panna cotta with the sauce on top.